What type of fitting should be used when joining dissimilar metals underground?

When joining dissimilar metals underground, the appropriate fitting to use is an insulating coupling or fitting. This type of fitting is specifically designed to prevent galvanic corrosion, which can occur when two different metals are in contact with each other in the presence of an electrolyte, such as moisture in the ground.

Galvanic corrosion happens because the two metals can create a small electric current between them, leading to the deterioration of one of the metals. Insulating couplings or fittings act as a barrier, effectively separating the two metals and minimizing the risk of corrosion. Additionally, they are constructed from non-conductive materials, ensuring that no electrical contact occurs between the dissimilar metals.

Using welded fittings, standard couplings, or compression fittings in this scenario would not adequately address the risk of galvanic corrosion, as these types of fittings do not offer the necessary insulation to prevent electrochemical reactions between the metals in question.